Surface Modified Boehmite Aluminas: A Versatile Approach to Nano-scale Particle Dispersion and Nanocomposites
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Surface Modified Boehmite Aluminas: A Versatile Approach to Nano-scale Particle Dispersion and Nanocomposites
Steven L. Baxter Lake Charles Chemical Complex, SASOL North America Inc., 2201 Old Spanish Trail, Westlake, LA 70669, U.S.A. ABSTRACT Certain forms of monohydrate aluminum oxide, commonly known as boehmite or pseudoboehmite alumina, are known to disperse in water at low pH to nano-scale dimensions. The upsurge of interest in nano-scale structures has prompted our study of the surface modification of nano-scale boehmite aluminas with organic acids in order to achieve dispersion of these materials in non-aqueous systems and alkaline aqueous systems. This paper discusses the variety of modifiers used to achieve compatibilization and dispersion of nano-sized particles of these boehmite aluminas in aqueous and organic matrices. Organic modification of a variety of crystallite sizes (5-60 nm) and shapes (plates, needles, blocks) has been achieved, including materials of high aspect ratio. We describe the properties of these dispersions, including primary particle size, dispersed particle size, and surface charge. Finally, we present physical property data of polymer nanocomposites prepared from these materials. These materials are based on a commercial process which has been in operation for over 40 years and which has global production capacities of 70,000 tons per annum.
INTRODUCTION The properties and behaviors of nano-scale materials have been extensively reported in the past few years, especially in polymer systems.1,2 This relatively new field of study is exploring structures intermediate in size between the atomic scale and the micro scale. Certain forms of monohydrate aluminum oxide, commonly known as boehmite or pseudoboehmite alumina, have been known for some time to disperse in water to nano-scale dimensions.3-5 The upsurge of interest in nano-scale structures has prompted this study of the surface modification of nanoscale boehmite aluminas with organic molecules in order to extend their applicability into nonaqueous systems and alkaline aqueous systems.
EXPERIMENTAL DETAILS Products were obtained by addition of the surface modifier to aqueous dispersions of the boehmite alumina, followed by spray drying. The dried powder was redispersed by addition to stirring solvent with gentle mixing (magnetic stir bar) at room temperature. X-ray diffraction data were acquired on a Bruker axs D4 Endeavor diffractometer. Zeta potential and dispersed particle size were measured with a Brookhaven Zeta Plus Zeta Potential Analyzer at high dilution. TEM work was performed on a JEOL 2010 at 200 kV and carried out by Texas A&M University’s Microscopy and Imaging Center. Samples were prepared by freeze-drying.
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RESULTS AND DISCUSSION Boehmite Alumina Structure A variety of impure hydroxides of aluminum occur in nature, primarily as bauxite. Boehmite, the common name for one of the mineral forms of the hydroxyoxide of aluminum, is readily available in relatively pure form by hydrolysis of aluminum alko
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